1. Field of the Invention
The invention relates to a gas pressure container, and more specifically, to a gas pressure container for an airbag system of a motor vehicle, as well as to a tube element for a gas pressure container and to a method for producing the same.
2. Description of the Related Art
A generic gas pressure container is described in EP 1 983 065 A1. The gas pressure container for an airbag system includes a tube element with a high bursting resistance when internal pressure is applied, wherein the tube element consists of a steel alloy and is to comprise a transition temperature of at least minus (−) 40 degrees Celsius (° C.) in a first longitudinal portion, and the tube element includes a second longitudinal portion and a third longitudinal portion which extend axially from the first longitudinal portion in the direction of two oppositely situated ends of the tube element. The longitudinal portions are realized in one piece and in one material from a seamless or welded, heat-rolled and/or cold-drawn tube, wherein the second longitudinal portion and the third longitudinal portion comprise an outer circumference which is reduced compared to the outer circumference of the first longitudinal portion. In order to ensure the high bursting resistance even in the case of low temperatures, the publication proposes hardening and tempering the finished tube element completely, that is to say after reducing the outer circumference in the second and third longitudinal portions, such that there is a uniform metallic microstructure with predominantly tempered martensite in the entire tube element of the gas pressure container and a tensile strength which is greater than 700 Megapascal (MPa) in the non-reduced central longitudinal portion.
However, it is a disadvantage that the geometrical accuracy and the surface quality are reduced as a result of the tempering of the tube element which tapers at the ends. In addition, as a result of reducing the outer circumference of the second and third longitudinal portions in the cold-drawn state, the cold formability and the bursting resistance are negatively influenced compared to the non-reduced first longitudinal portion.
In addition, US 2002 040 907 A1 describes a gas pressure container with a tube element produced from steel, the tube element being deep-drawn in multiple steps from a metal sheet and, in this case, a last longitudinal portion only being drawn in one step and then one longitudinal portion, in particular a transition region between longitudinal portions which have been drawn at variable frequencies, being subject to heat treatment. A targeted energy intake along with the termination of the start of an axial crack is to be brought about during the test as a result of the heat treatment. The bursting resistance of deep drawn tube elements, however, in spite of multiple heat treatments, are insufficient for present demands which are characterized by requirements for lightweight construction and accompanying thinner wall thicknesses of higher strength steels.